I decided to update my search by adding a little AJAX support via Michael Schwarz’s Ajax.NET library. When implementing the Ajax.NET library within a user control, I found that the suggested method of registering you class with the library in the Load event doesn’t work properly. While the library does emit the Javascript references to the HTTP handler (the purpose of registering your class with the library), invoking a call to the proxy didn’t work correctly. This only appeared to be an issue with user controls, regular .aspx pages work correctly. By directly including the two references to the handler within the HTML of the user control everything worked fine.